Hot Beds And Marrow Clamps.
What is a hot bed and how do I set one up?
Hot beds were very popular in Victorian times.Once set up, they can be used to grow salad crops in winter,get a head-start on seed sowing in the spring (by up to a month),and for growing melons and any of the cucurbitaceae family in the summer.A hot bed provides bottom heat,using manure rather than electricity as the heat source, thus speeding up plant growth of seedlings and tender plants.
• The Container: traditional a cold frame was used with the manure being stacked inside however other methods include digging a square pit and construction a clamp type structure by cutting 2 shipping pallets in half and placing them on top of the soil to form a square box.
• The heat source: Fresh strawy manure – in a layer 60-90cm deep (after treading). As the manure breaks down, it generates heat. Tread it down well to compact it, ensuring a more even release of heat. To get it started its a good idea to add a handful of general garden fertilizer per cubic metre of manure.
• The growing medium: A mixture of top soil and garden compost (ratio of 1:1) or organic compost – this is placed on top of the manure in a layer 20cm-30cm thick.
The depth of manure to growing medium is ideally 3:1. If you do decide to make the hot bed deeper, temperatures may rise above the optimum (24C) and plants may be scorched. It can be cooled down by adding water or leaves and garden debris to the mixture. Check temperatures daily with a thermometer.
A hot bed can be made in a greenhouse or outdoors. If you have used pallets to construct a clamp type structure you can pack straw or old newspaper down the side to help with insulation. Once filled cover with some plastic sheeting or in the case of a cold frame replace the top. Then leave for a week to 10 days for the hot bed to warm up.
Seed can be sown direct in the soil layer, or in trays placed on top. After building your hot bed in January, small seeded crops like salad and radish can be directly sown into the layer of compost or soil and compost on the top. A head start can be made by sowing trays of peas, beans, turnip and autumn cauliflower in trays or pots in Mid February. Courgettes and marrows can be directly planted in to the bed April/May. Salad crops are the best as they will grow quickly and take full advantage of the heat.
Maintaining the heat
A hotbed will only last for up to 2 months and then the contents will have to be removed and replaced i.e with fresh manure. During the period of use the temperature can be regulated by adding water with a watering can with a fine rose to reduce the temperture or to increase it covering with a plastic sheet, bell jars or with some old sacking/carpet over night to help the heat build up. The later is useful if a frosty night is expected.
Its worth having a try with several crops jut to see how you get on. One of the easiest is forced Rhubarb. This is done by digging up the crowns potting them into large pots, placing them on top of the hotbed/clamp and covering with forcing pots to encourage the growth of the shoots. .
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